The invention pertains to apparatuses for processing metals, rubber, plastics, paper and the like, in which a pressure applying element such as a roll or platen is employed to control the thickness and profile of the material. For the purpose of describing the invention without intention of limitation its use in a rolling mill has been selected.
The usual and customary type of rolling mill consisting of two vertical spaced apart housing posts for rotatively supporting a vertical stack of rolls, comprising usually between two to six rolls, inherently possesses two characteristics that result in undesirable gauge and profile rolled product deviations. These two well known limitations have reference to "varying mill stretch" and "varying roll bending", the former referring to the spring of the mill parts caused by the varying rolling force and the latter to the deflection of the rolls between their supported ends, again as a result of the varying rolling force.
These fundamental equipment limitations have been well recognized since the inception of the vertical stack rolling mill design and there has been a continuous effort made in many and sundry ways to lessen or eliminate the adverse affects. Notwithstanding, there still remains today a critical need to improve on prior attempts and particularly as current and future increased product quality is considered.
As reflected in past efforts, critical to improved results is some form of measuring device for determining as quickly, accurately and reliably as possible the rolled gauge and/or profile of the material. By way of a brief explanation of these terms, which are well recognized in the industry, by gauge it is meant to refer to the longitudinal thickness of the rolled material, such as a steel strip or plate taken on a given longitudinal axis of the strip, and by profile the cross sectional thickness of the strip, at several transverse points. In the context of this discussion these strip characteristics are the result of and caused by the act of rolling as distinguished from the condition of the strip having these characteristics before it is introduced into the roll bite.
Examples of such devices include X-ray gauges for measuring strip profile and gauge. All of these devices are located adjacent to the mill but at a distance downstream of the roll bite. Included in each profile system is a control system for initiating corrective action by well known means such as roll bending, variable crown back-up rolls, roll shifting-crossing, zoned roll cooling sprays, etc.
All of the above devices and systems were subject to three important limitations, all involving transport times, namely the time involved in the strip passing from the roll bite to the measuring device, the time the control takes to determine what action is to be taken and to initiate appropriate corrective action, and the time the means for effecting the corrective action takes to accomplish it. These drawbacks are exasperated by the fact that the usual X-ray gauges are arranged after the last stand of the tandem mill so that there is no opportunity to effect correction on a stand by stand basis.
In addition to the above noted problems surrounding profile considerations, separate and additional problems are found in prior art gauge control systems i.e. some form of the BISRA Automatic Gauge Control (AGC), that employ some part of the rolling force in determining and correcting for gauge variations. These systems include a rolling force signal in the form of a feedback signal, the rolling force being measured by load cells and/or pressure transducers, the latter associated with the roll gap actuator hydraulic cylinders and which systems suffer from the well known mill phenomena of modulus variation and hysteresis and roll eccentricity that result in production of off-gauge strip.